1. Field of the Invention
The present invention relates to a process of producing citrates and more particularly to the process of producing -- by means of extraction -- alkali metal or ammonium citrates from citric acid solutions produced by chemical methods or by fermentation.
2. Description of the Prior Art
Processes of producing alkali metal citrates from fermentation solutions have been described heretofore. It is known, for instance, to precipitate the citric acid by means of milk of lime, i.e. an aqueous suspension of calcium hydroxide, and subsequently reacting the resulting calcium citrate with an alkali metal carbonate. After removing the precipitated calcium carbonate, a trisodium citrate solution is obtained.
Alkali metal citrates have also been produced by directly neutralizing citric acid solutions. In this case, however, it is necessary to employ citric acid solutions in a substantially pure form. Both known methods are complicated and require many expensive and time consuming process steps.
It is also known to recover citric acid from its aqueous solution by means of extracting agents. Butanol-2 is used as extracting agent according to French Pat. No. 1,211,066, while German Published application No. 1,268,088 employs tri-n-butyl phosphate in mixture with hydrocarbons, ethers, esters, or ketones for this purpose. However, it was not possible to obtain satisfactory results with these known methods of extraction because the distribution coefficient in both described extraction processes is so low (about 1.0) that large amounts of the extracting agents and many extraction steps were required.